Currently Bluetooth radio communication devices detect other similar radios in the area by performing a Device Discovery procedure that includes the Inquiry procedure. The Bluetooth radio communication device sends an Inquiry message to which other Bluetooth devices in the area respond with an FHS packet.
Other communication devices measure energy on a communication channel and use this to predict possible radios in the area, but this method does not give any information of how the radio channel is being used. There are not even guarantees that the predicted radios actually exist. Furthermore, this process does not detect receiving radios.